Method of increasing the uniformity of cellulose esters



Patented May 7, 1929.

UNITED STATES I 1,711,941 PATENT OFFICE.

HARRY LE B. GRAY, OF ROOHESTER, NEW YORK, ASSIGNORiTO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A 'OORPORATION1 OF NEW YORK.

METHOD OF INCREASING THE UNIFORMITY F CELLULOSE ESTEBS.

No Drawing.

This invention relates to methods of increasing the uniformity of cellulose esters. One ob ect of the invention is to provide a method which is relatively simple and inexpensive to carry out, and et mixes the ingredients so thoroughly t at esters of great uniformity, especially in their solubilities, are produced. Another object of the invention is to impregnate the cellulosic l0 material or fibers, prior to esterification, very uniformly, even when the-proportion of acylating liquid, relative to the cellulose, is small. Other objects will hereinafter appear.

It is highly desirable in the manufacture of cellulose esters of organic acids to obtain products which are of high uniformity in their solubility. Thisuniformity is greatly dependent upon the thoroughness with which the acylating liquid is mixed with the cellulosic fibers prior to esterification; For example, in making cellulose acetate, it is desirable to obtain uniform acetylation throughout all parts of the fibers, so that all of such parts will be soluble in chloroform,

and ultimately in acetone. This avoids the resence of insoluble particles which cause a liazy appearance in solutions or films made from the esters.

One of the principal well known ways of mixing the cellulosic material and the reacting liquid is to immerse the cellulosic fibers in an excess of the liquid, Sometimes the excess of liquid is allowed to remain dur-,

At other times the excess of liquid is removed, say by ing the esterification reaction.

pressure, and only a smaller proportion of the liquid stays behind in the fibers to effect the estetrification. It hasbeen found that there is ia noticeable tendency for nonuniform mixing to occur under these conditions. Each fiber of the cellulosic material is not fully wetted with the organic esterifying liquid, and a non-uniform product results, from which hazy films are produced. The lack of uniformity may be partly due to air that is trapped along the. fibers 1n the form of small bubbles, or to surface repellency of-the fibers toward the esterfying liquid.

I have found that esters of high uniformity may be prepared and the effects of air bubbles and surface repellancy may be successfully combatted by mixing the acylating liquid with a volatile, substantially non-re- Application filed August 25, 1927. Serial No. 215,519.

acting solvent vehicle, incorporating this mixture with the cellulosic fibers and then remoying the vehicle by evaporation or distlllation under a vacuum. In'the preferred form of my invention the fibers are first placed under a vacuum, and then the mixture of acylating liquid and the liquid vehicle are run into the fibers while the vacuum is maintained. Then the vehicle is removed under vacuum, the vacuum is broken and esterification allowed to proceed under normal conditions at or above atmospheric'pressure. 1

My invention is applicable in connection with any of the cellulosic fibers which are useful in making cellulose esters of organic acids. the most important of such esters, I shall describe, by way of illustration, the use of acetylating liquids in carrying out my proc- Since cellulose acetate is at present ess; but it will beunderstood that my invention is applicable to any similar organic acylating liquids, such, for instance, as those described in the applications of Hans T. 1

Clarke and Carl J. Malm, Serial Nos. 179,- 176 and 179,177 for process of making organic esters of cellulose containing acyl groups having more than two carbon atoms, and process of making cellulose esters of organic acids, both filed March 28th, 1927. Instances of such liquids include acetic anhydrid with any of lauric,myristic, palmitic or stearic acid; chloracetic anhydrid with. stearic or formic acid.

For the liquid vehicle'an of the relatively inexpensive volatile organic solvents, which do not substantially react with the other ingredients of the reaction mixture, may be employed. Chloroform or ether may be successfully used, for instance. The removal ofthe liquid vehicle from the mixture-under a vacuum by eva oration is carried out at a temperature su ciently low to hold back the esterification reaction during the removal of the vehicle.

- the cellulosic material is mixed with a relatively small proportion'of acetylating liquid. It is particularly difiicult to mix such a small proportion of such liquid, with the fibers to obtain the necessar uniformity. My pressent method ena les even very small amounts of the'esterifying liquid, such as acetic anhydrid, to be distributed with the" utmost uniformity throughout the cellulosic fibers.

For example 100 parts by weight of clean cotton fibers, say filter cotton, are placed under a vacuum of 14 to 4Q millimeters of mercur There is then added to the fibers, while t ey are still under a vacuum, a mixture of 220 parts of acetic anhydrid (94% strength), 1800 parts of chloroform by weight, and .25 parts by weight of sulfuric acid and .25 parts by weight of phosphoric acid. The liquid mixture, including the chloroform, is sufficient in quantity to thoroughly and uniformly wet every fiber. Then while the vacuum is kept up the l chloroform is allowed to evaporate, and its vapors are recovered by condensation or abtreatment.

from the reaction mixture fully dissolve in.

pure chloroform. The end of the reaction may likewise be found by examining test specimens by polarized light, using a microsco e arranged with crossed Nicols prisms an a selenite plate so located as to give the most brilliant red field. During the acetylation, the fibers change from brilliant yellow to a deep red or blue,dependin upon the position of the fibers relative to t e plane of polarization of the light. The fully acetylated fibers, under these conditions, retain .their fibrous appearance without dissolving,

orcoming together so as to be diflicultly manipulatable in the subsequent stages of.

. Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: I

1. The method of making cellulose esters of organic acids which comprises the steps of thoroughly mixing the cellulosic material to be esterified with aninert volatile organic liquid vehicle having dissolved therein the amount of acylating agent for the reaction and also carrying a catalyst,

evaporating said vehicle under a vacuum from the mixture, thereby leaving said acylating agent and catalyst uniformly distributed throughout said fibers, breaking the vacuum and conducting the esterification reaction.

2. The method of making cellulose esters of organic acids which comprises the steps .of placing the cellulosic fibers-to be esterified under a vacuum, thoroughly mixing said fibers While maintaining avacuum, with an inert volatile organic liquid vehicle having dissolved therein the amount of acylating agent for the reaction and also carrying a catalyst, evaporating said vehicle under vacuum fromthe mixture, thereby leaving said agent and catalyst uniformly distributed throughout said fibers, breaking the vacuum and conducting the esterification reaction. Y

3. The method ofmaking cellulose acetate which comprises the steps of thoroughly impregnating cellulosic fibers with an inert volatile organic liquid. vehicle having dissolved therein the amount of. acetic anhydrid for the reaction and a catalyst, evaporating said vehicle under vacuum from the mixture, thereby leaving said anh drid and catalyst uniformly distributed t iroughout said fibers, breaking the vacuum and conducting the acetylation;

4. g The method ofmaking cellulose acetate which comprises the steps of placing the cellulosic fibers to be esterified under a vacuum, mixing said fibers while maintaining a vacuum, with an inert volatile organic liquid vehicle having dissolved therein the amount of acetic anhydrid for the reaction and also carrying a catalyst, evaporating said vehicle under vacuum from the mixture, thereby leaving said anhydrid and catalyst uniformly distributed throughout said fibers, breaking the vacuum and conducting the acetylation. I

Signed at Rochester, New York, this 19th day of Aug, 1927.

i HARRY LE B. GRAY. 

